1. Field of Invention
The present invention relates generally to the field of network content delivery and bandwidth utilization. More particularly, the present invention is directed to efficient multicasting of packetized content in a system incorporating multiple physical channels.
2. Description of Related Technology
Modern cable networks deliver both audio and video programming as well as Internet access. These services are typically provided via a set of radio frequency channels transmitted through coaxial cable to the subscriber's premises. The use of fiber optical cable is also known, and often both are incorporated in the cable network (Hybrid Fiber Coaxial—“HFC”), however the dominant form of the delivery into the home (the last mile) remains the coaxial cable.
To receive the various services provided by the cable network the customer is often provided with, or required to obtain, customer premises equipment (CPE). For video and audio programming the CPE is typically referred to as a “set top box” or STB The set top box traditionally sat on top of, or in proximity to, the television set, hence the name. For Internet services, the CPE is typically a cable modem (CM). The cable modem modulates and demodulates the RF signals exchanged with the cable network.
Both the cable modem and the set top box receive the set of RF channels delivered over the coaxial cable network. This set of RF channels typically comprise a subset of RF channels dedicated to the transmission of audio and video information, and a subset of RF channels dedicated to the delivery of Internet or other data services.
For the delivery of Internet service, the cable modem is tuned to one of the RF channels dedicated to providing the Internet service. The cable modem processes the signals on the RF channel, and forwards the traffic (e.g., Internet protocol or IP packets) to the requesting device or network on the customer premises, as well as allowing packets to be sent upstream from the consumer's premises.
Different groups of cable modems are typically assigned to different RF channels in order to distribute the traffic more evenly, or achieve other operational goals. In general, assigning different RF channels to different modems is an efficient method of distributing traffic across the network.
However, as a DOCSIS cable modem (pre-DOCSIS 3.0), is typically limited to a theoretical maximum of approximately 40 Mbps of data throughput in the downstream direction (i.e., from head-end or hub to CPE), the number of video programs that can be broadcast to a given CPE device connected to that CM is limited. For example, if a video program consumes 1.5 Mbps, then at most, 26 programs 1.5 Mbps×26=39 Mbps) could be received at any one time, ignoring for present purposes any overhead associated with packet headers, etc. As this 40 Mbps is the limit not only for the single modem, but for all modems sharing the same DOCSIS downstream port on a typical CM termination system (CMTS), the number of simultaneous video programs broadcast to a given neighborhood served by one CMTS port would be limited to 26 programs. Given that a typical modern cable video channel lineup consists of hundreds of different channels, and that high definition (HD) content consumes more than 1.5 Mbps, the entire channel lineup cannot be replicated on a single DOCSIS 2.0 downstream channel, given currently acceptable video encoding bitrates. Even a hypothetical future cable modem capable of 100 Mbps could not support such a broadcast.
Alternatively, multiple DOCSIS downstream channels could be utilized in order to transmit all of the aforementioned channels simultaneously. Given a theoretical 200 channel lineup where each video channel is encoded at 1.5 Mbps, and each DOCSIS channel carries 26 programs, then 8 DOCSIS downstream channels (8 channels×26 programs/channel=208 programs) would be needed to replicate the video broadcasts over DOCSIS. As a DOCSIS 2.0 CM is only capable of tuning to a single DOCSIS downstream channel at any one time, and assuming that there would be multiple user devices (e.g., TV sets) in use simultaneously in a single premises served by a single CM, it is likely that all desired programming for that premises would not be residing on a single DOCSIS downstream channel. Hence, the premises could not receive all of the desired programs simultaneously.
Multicast Traffic
More recently, networks have incorporated the use of multicast Internet traffic or multicast Internet Protocol (IP) transmissions. Multicast Internet traffic is traffic directed from one point to many, which is useful for broadcast type services such as video or audio streaming.
In the day-to-day operation of a cable network, it is often the case that two cable modems will receive the same multicast transmission. In some instances, the two cable modems will be assigned to receive Internet traffic on two different RF channels. In that case, both RF channels will have to transmit the same multicast transmission.
The traditional video content described above is typically MPEG-based video. Video transported to PCs (or IP-based devices such as STSs) over a DOCSIS network is typically MPEG (or another video codec)-over-IP over MPEG. That is, the higher layer MPEG- or other encoded content is encapsulated using an IP protocol, which then utilizes an MPEG packetization for delivery over the RF channels used by a DOCSIS device such as the aforementioned cable modem. If the multicast comprises such a video or other sizable transmission, the amount of network bandwidth consumed may be substantial. This “wasted” bandwidth reduces the overall efficiency of the cable network.
A variety of different approaches to unicast and multicast packet data delivery over networks, including content-based (e.g., cable) networks, are present in the prior art. For example, U.S. Pat. No. 6,181,697 to Nurenberg, et al. and issued on Jan. 30, 2001 entitled “Method for a unicast endpoint client to access a multicast internet protocol (IP) session and to serve as a redistributor of such session” discloses a endpoint client on an IP Unicast network that is provided access to a Multicast session on an IP Multicast network through a Multicast-Unicast gateway server (MUS) which is enabled to re-Multicast that session to other endpoint clients on the network to which it is connected or to endpoint clients on any Multicast-capable sub-network to which it is directly connected. To act as a re-Multicaster, the endpoint client receiving Unicast-addressed packets from the session from the MUS, re-translates these Unicast-addressed packets to Multicast-addressed packets by translating the Unicast address in the distribution field of each packet's header into a Multicast address and overwriting the Unicast address in each header with the Multicast address. When an endpoint client on the same or connected sub-network as the re-Multicaster desires to join a session that is being re-Multicast, it needs only connect to that Multicast address. A endpoint client on a Unicast network can elect to be a re-Multicaster of packets from a session as long as that same session is not being re-Multicast by another endpoint client on any sub-network on which the electing re-Multicaster is connected or a Multicast router is not forwarding packets from the session onto the sub-network.
U.S. Pat. No. 6,259,701 to Shur, et al. issued Jul. 10, 2001 and entitled “Method and system for a unicast endpoint client to access a multicast internet protocol (IP) session” discloses unicast endpoint clients on an IP Unicast network which are provided access to Multicast sessions on an IP Multicast network through a Multicast-Unicast gateway server. The server obtains information about sessions on the Multicast network and makes such information available to a Unicast client on the Unicast network upon request by the client. Upon being presented with a list describing the subject matter of each session, the user at the Unicast client selects the session to which he or she wants to join, which causes the Multicast-Unicast server to join the appropriate session on behalf of the requesting client for each media type in which the joining client wants to be a participant. The server then sets a bidirectional Unicast User Datagram Protocol (UDP) stream between itself and the client. All packets then received by the server from the Unicast client are address-translated to the appropriate Multicast session address. In addition, all packets received by the server on the Multicast session address are address-translated and sent to the Unicast client. The Unicast client is then able to participate in the Multicast session as both a sender and a receiver of packets to and from other Unicast and Multicast clients which are active during the session. Further, the Unicast client is capable of creating a new session, recording a session in the network for later retrieval and playback, and creating and accessing low bandwidth versions of existing sessions.
U.S. Pat. Nos. 6,925,257 and 6,519,062 to Yoo both entitled “Ultra-low latency multi-protocol optical routers for the next generation internet” disclose an ultra-low latency optical router with a peta-bit-per-second total aggregate switching bandwidth, that will scale to a total connectivity of 1000 by 1000, and beyond by modular upgrades. The unit serves as an engine to other optical routers that can function in the context of circuit-switching, flow-switching, burst-switching, and packet-switching. The unit uses advanced wavelength conversion technology to achieve three methods of contention resolution in the router: deflection in wavelength, deflection in space, and buffering in time, and that interfaces a local network to the Supernet.
United States Patent Publication No. 20010004768 to Hodge, et al. published Jun. 21, 2001 entitled “Highly integrated computer controlled digital head end” discloses a highly integrated computer controlled digital headend configured to process a plurality of digital video, a plurality of digital data, a plurality of voice information, and a plurality of upstream communications. The digital headend includes at least one smart network interface module operatively coupled to a shared bus, a downstream module and an upstream module. Preferably, the smart network interface module is configured to receive, transfer and buffer the plurality of digital video, the plurality of digital data, the plurality of voice information and the plurality of upstream communications. The shared bus is operatively coupled to the at least one smart network interface module. The shared bus is configured to transport the digital video, the plurality of digital data, the plurality of voice information, and the plurality of upstream communications. The downstream module is operatively coupled to the shared bus. The downstream module is configured to transmit the plurality of digital video, the plurality of digital data and the plurality of voice information.
United States Patent Publication No. 20010005908 to Hodge, et al. published Jun. 28, 2001 and entitled “Method for buffering video, data and voice signals using a common shared bus” discloses a method for combining a plurality of digital video signals, a plurality of digital data signals, a plurality of voice signals, and a plurality of upstream communications within a digital broadband headend. This digital broadband headend uses a common shared bus to optimize the resources used on a digital headend. More particularly, the method comprises providing a video interface for receiving the plurality of digital video signal, providing a data interface for receiving the plurality of digital data signals, and providing a voice interface for receiving the plurality of voice signals. The method then proceeds to process the plurality of digital video signals, digital data signals and voice signals. After this processing is completed by the digital headend, the plurality of digital video signals is communicated to at least one smart network interface module which is configured to buffer the plurality of digital video signals
United States Patent Publication No. 20020056125 to Hodge, et al. published on May 9, 2002 and entitled “Multi-tier buffering system and method which combines video, data, and voice packets” discloses a digital headend system for communicating a plurality of video packets, data packets, voice packets, and control packets. The system includes a buffering module, a re-packetization module, and a synchronization module. The buffering module receives the plurality of video packets, data packets, voice packets, control packets or any combination of packets. Preferably, the buffering module generates a destination address which identifies a particular re-packetization module. The identified re-packetization module is in communication with the buffering module. The first re-packetization module combines the plurality of video packets, data packets, voice packets, control packets or any combination thereof. The synchronizing module receives the re-packetization output and generates a synchronous output stream having the plurality of video packets, data packets, voice packets, control packets or any combination thereof. Preferably, the synchronous output stream is comprised of MPEG transport packets. The present invention also provides a method for communicating the plurality of video packet, data packet, voice packet, control packets, or any combination thereof
United States Patent Publication No. 20040045032 to Cummings, et al. published Mar. 4, 2004 and entitled “MiniMAC implementation of a distributed cable modem termination system (CMTS) architecture” discloses a miniMAC implementation of a distributed CMTS in a hybrid fiber/coaxial (HFC) plant. The distributed CMTS comprises at least one network layer, at least one media access layer, and one or more physical layers. The at least one media access layer includes one or more miniMAC layers. The one or more miniMAC layers are remotely located from a remaining part of the at least one media access layer. The at least one network layer, the remaining part of the at least one media access layer, the one or more miniMAC layers, and the one or more physical layers each function as separate modules, enabling each layer to be in separate component locations of the HFC plant, yet having the at least one network layer connected to the remaining part of the at least one media access layer, the at least one media access layer connected to each of the one or more miniMAC layers, and each of the one or more physical layers connected to each of the one or more miniMAC layers. The one or more miniMAC layers are located in close proximity to the one or more physical layers in the HFC plant. The one or more miniMAC layers convert digital bit streams into packets and maintain timing constraints between the one or more miniMAC layers and the one or more physical layers.
United States Patent Publication No. 20040045037 to Cummings, et al. and published Mar. 4, 2004 entitled “Distributed cable modem termination system (CMTS) architecture implementing a media access control chip” discloses a distributed cable modem termination system (CMTS) in a hybrid fiber/coaxial (HFC) plant. The distributed CMTS comprises a network layer, at least one media access control layer, and at least one physical layer. The media access control layer implements a media access control chip. The media access control chip interfaces with the physical layer to provide timing to maintain components within the physical layer. At least one physical layer is connected to a respective at least one media access control layer. The network layer, media access control layer, and physical layer each function as separate modules. The media access control chip does not require packet level media access control functions to be implemented in the same physical location. See also United States Patent Publication No. 20040045035 to Cummings, et al. published Mar. 4, 2004 entitled “Distributed cable modem termination system (CMTS) architecture, ” and
United States Patent Publication No. 20050002331 to Nolle, et al. published Jan. 6, 2005 and entitled “Predictive upstream load balancing” discloses the static balancing of cable modems across upstream channels which are made based on the channel's current bandwidth demand compared to a first and/or second CAC threshold level. If both threshold levels are exceeded, the modem is assigned to the channel having the lowest bandwidth demand. After registration, predictive balancing modems according to whether an MTA is part of a given modem avoids concentration of modems having MTAs on certain channels while other channels serve only modems without MTAs. Modems are also predictively balanced according to whether they have associated a DSA_use_history profile. Modems associated with certain subscribers may be balanced according to the time of day balancing is occurring based on the profile. Thus, light user's during working hours may be balanced as heavy user's at night if they typically download video content or use VoIP features during the evening— 
“Switched” Architectures
One emerging technology useful for efficiently delivering video and other content to network subscribers comprises so-called “switched” or “broadcast switched” architectures. These systems make use of the fact that while a given number of channels of programming or content must be made available to a given pool of subscribers, not all of these channels (and in fact, not even most of these channels) are required to actually be delivered to subscribers at any given time. Rather, only a fraction of these channels are requested. Hence, the use of “intelligent” and prompt switching of these channels can obviate the need to deliver all of the channels simultaneously; only those channels actually being viewed or requested are switched onto the QAMs for delivery to the appropriate subscribers.
However, such switched functionality has heretofore only been applied to more traditional broadcast video as opposed to packetized IP media traffic, such as the multicast traffic previously described (which includes so-called “IP-TV”).
Despite the foregoing wide variety of packetized media processing and delivery techniques evidenced in the prior art, there is still a salient need for improved apparatus and methods for distributing multicast IP or other packetized content over a content-based (e.g., cable) network in an efficient and flexible manner. Such apparatus and methods would ideally leverage existing infrastructure and require little in the way of network modification in order to be implemented, yet provide network operators with the ability to deliver multicast traffic (including relatively high bandwidth video content) to multiple network users without monopolizing numerous downstream channels.
The improved apparatus and methods would also ideally be adaptable to varying types of network architectures, including those of the digital “switched broadcast” variety, and leverage the inherent attributes of these networks to provide even more efficient delivery of packet services.